1. Technical Field
This invention relates generally to a device for use in separating an implanted elongated structure from encapsulating tissue in the body of a patient. More particularly, the invention relates to a tip for an extraction device for use in separating a cardiac lead from encapsulating biological tissue.
2. Background Information
A variety of medical treatments and surgical methods entail implanting an elongated structure in the body of a patient. Examples of such elongated structures include catheters, sheaths and cardiac leads (such as pacemaker leads and defibrillator leads), as well as a variety of other devices. Over time, it can become necessary or desirable to remove the implanted elongated structure from the body of the patient. However, if the elongated structure has been implanted for an extended period of time, encapsulating biological tissue can grow around the elongated structure, making it difficult to remove the structure from the encapsulating tissue.
A heart pacemaker is typically implanted in a subcutaneous tissue pocket in the chest wall of a patient. A pacemaker lead extends from the pacemaker through a vein into a chamber of the patient's heart. The pacemaker lead commonly includes a conductor, such as an electrical wire coil, for conducting electrical signals (such as stimulating and/or sensing signals) between the pacemaker and the heart. Leads for defibrillators are generally similar to pacemaker leads, and are positioned about the heart. Defibrillator leads may be affixed either internally or externally of the heart.
While cardiac leads typically have a useful life of many years, over time such leads may become encapsulated by fibrotic tissue against the heart itself or the wall of the vein, against other surrounding tissue, or even against other cardiac leads in the vein. Encapsulation is especially encountered in areas where the velocity of the flow of blood is low. The fibrotic tissue can be very tough, which makes it difficult to remove the lead from the area of the heart without causing trauma to the area. When small diameter veins through which a cardiac lead passes become occluded with fibrotic tissue, separation of the lead from the vein can cause damage to the vein, including the possible dissection or perforation of the vein. In such cases, separation of the lead from the vein is usually not possible without restricting or containing movement of the lead, i.e., fixing the lead in position with respect to the patient, in particular, with respect to the patient's vein.
To avoid this and other possible complications, some useless or otherwise inoperable cardiac leads are simply left in the patient when the pacemaker or defibrillator is removed or replaced. However, such a practice can incur the risk of an undetected lead thrombosis, which can result in stroke, heart attack, or pulmonary embolism. Such a practice can also impair heart function, as plural leads can restrict the heart valves through which they pass.
There are many other reasons why removal of an inoperable lead may be desirable. For example, if there are too many leads positioned in a vein, the vein can be obstructed to the extent that fluid flow through the vein is compromised. In addition, multiple leads can be incompatible with one another, thereby interfering with the pacing or defibrillating function. An inoperable lead can migrate during introduction of an adjacent second lead, and mechanically induce ventricular arrhythmia. Other potentially life-threatening complications can require the removal of the lead as well. For example, removal of an infected cardiac lead may be desirable so as to avoid conditions such as septicemia or endocarditis. Finally, such removable may be desirable so that the space occupied by the inoperable lead in the vein could be better utilized, e.g., by the presence of a new lead.
Surgical removal of a heart lead in such circumstances may require open heart surgery. However, open heart surgery is accompanied by significant risk and cost to the patient, as well as a potential for unintended complications. A variety of methods and apparatuses have been devised as alternatives to open heart surgery for heart lead removal. Several of these methods and apparatuses are described in related patents and publications, such as U.S. Pat. No. 5,697,936, titled “Device for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,507,751, titled “Locally Flexible Dilator Sheath”; U.S. Pat. No. 5,632,749, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,207,683, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 4,943,289, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,011,482, titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Pat. No. 5,013,310, titled “Method and Apparatus for Removing an Implanted Pacemaker Lead”; U.S. Pat. No. 4,988,347, titled “Method and Apparatus for Separating a Coiled Structure from Biological Tissue”; U.S. Pat. No. 5,423,806, titled “Laser Extractor for an Implanted Object”; U.S. Pat. No. 6,419,974, titled “Radio Frequency Dilator Sheath”, U.S. Pat. Nos. 6,687,548 and 6,712,826, each titled “Apparatus for Removing an Elongated Structure Implanted in Biological Tissue”; U.S. Patent Publ. No. 2006/0235431, titled “Lead Extraction Device”' U.S. Patent Publ. No. 2006/0253179, titled “Tip for Lead Extraction Device”; U.S. Patent Publ. No. 2008/0071341, titled “Tip for Lead Extraction Device”; and U.S. Patent Publ. No. 2008/0071342, titled “Vessel Entry Device”; among others. Each of the aforementioned patents and patent publications is incorporated by reference as if fully set forth herein.
Many of the aforementioned patents and patent publications describe manual, or mechanical, devices that are used for removing an implanted structure, such as a cardiac lead. Others describe non-mechanical techniques, such as laser extraction and radio frequency extraction. Although the prior art devices have been found to be reasonably effective in many situations, physicians continue to encounter particularly challenging situations in which existing extraction devices may not provide satisfactory or consistent results. Due to the multiplicity of factors that may contribute to the difficulty in extracting an implanted lead, a technique that may be effective in one instance may not provide similarly successful results in another instance.
For example, manual devices normally are provided with a single rotating flexible sheath, or dual telescoping flexible sheaths, for tracking over the cardiac lead. Such sheaths are generally formed from a polymer, and have the flexibility to enable the sheath to traverse tortuous pathways in the vessel. However, such rotating sheaths may lack sufficient strength to cut through particularly tough tissue growth and calcification around the implanted lead. On some occasions, such devices are provided with a metallic tip at the distal end of the sheath, or at the distal end of the inner sheath in the dual sheath arrangement. As described in the incorporated-by-reference U.S. Patent Publication Nos. 2006/0253179, 2008/0071341, and 2008/0071342, the tip may include a generally helical or like structure protruding radially from the outer surface of the tip. Among other things, the radial protrusion often improves the ability of the tip to core or otherwise non-cuttingly disrupt the encapsulating tissue from the lead as the rotating sheath and tip advance through the vessel. However, on some occasions, the presence of a radial protrusion along the outer surface of the tip may promote lead wrap; e.g., the undesired wrapping of another implanted lead in the vessel around the rotating tip or around the implanted lead targeted for removal.
Laser and radio frequency devices normally utilize metallic sheaths. Such sheaths typically provide a good deal of strength to enable the sheath to cut through fibrous growths. However, some growths are resistant to metallic sheaths. In addition, these sheaths may lack the flexibility desired to maneuver tortuous pathways. Laser and radio frequency systems can also be expensive, particularly when compared to mechanical devices. Further, many facilities lack the equipment necessary to carry out these techniques.
It would be desirable to provide a device and tip structure that is effective for removing implanted leads from a vessel, that is easy to operate, and that is versatile enough to overcome many of the obstacles that may be encountered in such operations with existing devices.